Theorem 1z

Description: One is an integer. (Contributed by NM, 10-May-2004)

	Ref	Expression
Assertion	1z	⊢ 1 ∈ ℤ

Proof

Step	Hyp	Ref	Expression
1		1nn	⊢ 1 ∈ ℕ
2	1	nnzi	⊢ 1 ∈ ℤ